As for an apparatus used for manufacturing semiconductor devices, there has been known a so-called single-wafer processing apparatus for performing a process on a substrate one by one. Specifically, the process may include a plasma process such as a CVD (chemical vapor deposition) process or an etching process, or heat treatment such as a thermal CVD process. Generally, since the apparatus is configured to perform such processes under a vacuum atmosphere, a mounting table is provided in a processing chamber as a vacuum chamber and a gas shower structure is configured to dispose so as to face the mounting table and supply a processing gas onto a substrate, as in a shower device.
FIG. 10 is a schematic view for describing a general structure of a vacuum processing apparatus. In FIG. 10, a reference numeral 101 denotes a processing chamber; a reference numeral 102 denotes a mounting table for mounting thereon a substrate 103; a reference numeral 104 denotes a gas shower head serving as a ceiling plate of the processing chamber 101; and a reference numeral 105 denotes a gas exhaust line for performing evacuation. The gas shower head 104 may include a cover 106 for airtightly covering an opening formed on a top surface of the processing chamber 101 via a non-illustrated sealing member; and a shower plate 107. A processing gas is introduced into a diffusion space 109 through a gas inlet port 108 and the introduced processing gas is supplied through gas inlet holes 100 of the shower plate 107, as in a shower device.
The shower plate 107 is formed by stacking two plates made of different materials. A base plate 110 as an upper plate is made of a metal such as aluminum (Al) or stainless steel (SUS). A ceiling plate 111 as a lower plate is made of silicon (Si), silicon carbide (SiC), quartz or the like. By using two plates, the shower plate 107 can be prevented from being deformed by stress caused by depressurization when a process is performed under a processing atmosphere in a vacuum level, and a portion of the shower plate 107 which is exposed to the processing atmosphere can be protected from metal contamination. Especially, in a plasma process, the plasma resistance of the shower plate 107 can be further improved by using the two plates.
As for a structure for joining the base plate 110 and the ceiling plate 111, there has been known a structure illustrated in FIGS. 11A and 11B, for example. In the structure of FIG. 11A, the outer periphery of the base plate 110 is protruded from the outer periphery of the ceiling plate 111. The base plate 110 and a ring-shaped clamp 112 are press-connected to each other via the ceiling plate 111 disposed therebetween by a screw 113. The clamp 112 is made of a metal, and the clamp 112 may include a portion facing the protruded portion of the base plate 110; and a portion covering a periphery of a rear surface of the ceiling plate 111. Meanwhile, in the structure of FIG. 11B, the base plate 110 and the ceiling plate 111 are joined to each other at the peripheries thereof by a screw 114 inserted from the ceiling plate 111.
However, in the structure using the clamp 112, since the base plate 110 and the clamp 112 are press-connected each other via the ceiling plate 111 by the screw 113, a gap is structurally required between the clamp 112 and the base plate 110. A pressing force is controlled as a screw torque by using this gap. Thus, the screw torque needs to be controlled strictly such that the screw 114 is prevented from being excessively tightened or loosened, and assembly errors may lead to non-uniformity of performance (non-uniformity of the pressing force). Further, the clamp 112 is made of a metal because the metal can be easily processed. However, since the ceiling plate 111 and the clamp 112 are made of different materials, a thermal expansion difference therebetween causes friction at a contact area S. Accordingly, particles may be generated at the friction area and introduced into the processing atmosphere.
A temperature of the shower plate 107, which is an important process parameter, is controlled by a unit above the shower plate 107, e.g., outside of the gas shower head 104. Since, however, the gap is formed between the clamp 112 and the base plate 110, a thermal conductivity therebetween is decreased. Further, when the shower plate 107 is used as an electrode in a plasma process, an electrical conduction becomes poor. If the thermal conductivity or an electrical conduction become poor, the uniformity of the heat or an electric field between the shower plate 107 and a vicinity thereof is decreased, resulting in deteriorating the uniformity in a surface of the substrate in the plasma process.
Meanwhile, in the structure of FIG. 11B, the base plate 110 and the ceiling plate 111 are press-connected each other by the screw 114, so that the screw torque needs to be controlled strictly. Besides, the ceiling plate 111 and the screw 114 are respectively made of ceramic and metal as described above, and, thus, a screw hole needs to be formed at the base plate 110. Accordingly, the thermal expansion difference between the screw 114 and the ceiling plate 111 causes friction at a contact area S, which results in the above-described problems. Moreover, in order to protect a head of the screw 114, a ring-shaped cover may be formed around the ceiling plate 111 in a circumferential direction. In such a case, however, if the cover is scaled-up, selection of materials having a high plasma resistance is limited. In addition, since the gap exists between the cover and the ceiling plate 111, the screw 114 is damaged by plasma introduced through the gap. As a consequence, the loosening or breakage of the screw 114 may occur.
Patent Document 1 discloses a structure for joining a conductive plate having a plurality of holes and a support structure via an electrical-connection member having elasticity by a screw. However, the thermal conduction or the electrical conduction between the conductive plate and the support structure is locally carried out via the electrical-connection member, so that the conduction is not effective. Moreover, the thermal expansion difference between the screw and a spacer and between the spacer and the conductive plate causes friction, which may lead to introduction of particles into the processing atmosphere.
Patent Document 2 discloses a structure for joining a gas shower plate and a lower part of a high frequency electrode via a spiral-shaped metal tube. However, if a screw is inserted from the gas shower plate, the same problems of the structure shown in FIG. 11B may occur.    Patent Document 1: Japanese Patent Laid-open Publication No. 2001-135499 (FIG. 1)    Patent Document 2: Japanese Patent Laid-open Publication No. 2004-356509 (FIGS. 1 and 3)